DESCRIPTION: (as per applicant abstract) One of the most exciting advances in auditory prosthesis research in the last five years is the demonstration by our laboratory and others that speech recognition with cochlear implants can be significantly affected by the configuration of the electrical stimuli delivered to individual channels of the implant. The objectives of this proposal are to define the functional effects of specific spatial configurations of the electrical stimulus using speech recognition and psychophysical measures. We will expand on previous studies to define the processing strategies and types of stimuli for which various configurations of the electrical signal are most effective. Human subjects with Nucleus 22, Nucleus 24M and Clarion prostheses will be used. Psychophysical measures will include difference limens for pulse-rate, modulation-frequency, electrode-place, and intensity. Stimuli for speech-recognition testing will include phonemes, words, and complete sentences tested in quiet and in noise. The studies will be guided by models of the spatial extent and pattern of central neural excitation generated by specific electrical- current configurations. Psychophysical threshold, loudness, and gap detection data that have been proposed to reflect spread of neural activation will be obtained for the various configurations. This series of studies is expected to lead to improved performance in patients with cochlear implants by (a) influencing the procedures for fitting today's processors to individual patients and (b) guiding the design of electrode arrays and processors for the implants of the future.